Saturday, March 24, 2012

Stop Conficker from spreading via Group Policy

* Please carefully read and understand the below instructions. If unsure seek help from a professional.

* Read the notes below task 4 (Very important)

Task 1: Set a policy to remove write permissions to the following registry subkey: HKEY_LOCAL_MACHINE\Software\​Microsoft\Windows NT\CurrentVersion \Svchost This prevents the random named malware service from being created in the netsvcs registry value.

To do this, follow these steps: 1. Open the Group Policy Management Console (GPMC). 2. Create a new Group Policy object (GPO). Give it any name that you want. 3. Open the new GPO, and then move to the following folder: Computer Configuration\Windows Settings\Security Settings\Registry 4. Right-click Registry, and then click Add Key. 5. In the Select Registry Key dialog box, expand Machine, and then move to the following folder: Software\Microsoft\Windows NT\CurrentVersion\Svchost 6. Click OK. 7. In the dialog box that opens, click to clear the Full Control check box for both Administrators and System. 8. Click OK. 9. In the Add Object dialog box, click Replace existing permissions on all subkeys with inheritable permissions. 10. Click OK. Task 2. Set the policy to remove write permissions to the %windir% \tasks folder. This prevents the Conficker malware from creating the Scheduled Tasks that can re-infect the system.

To do this, follow these steps: 1. In the same GPO that you created earlier, move to the following folder: Computer Configuration\Windows Settings\Security Settings\File System 2. Right-click File System, and then click Add File. 3. In the Add a file or folder dialog box, browse to the %windir% \Tasks folder. Make sure that Tasks is highlighted and listed in the Folder: dialog box. 4. Click OK. 5. In the dialog box that opens, click to clear the check boxes for Full Control, Modify and Write for both Administrators and System. 6. Click OK. 7. In the Add Object dialog box, click Replace existing permissions on all subkeys with inheritable permissions. 8. Click OK.

Task 3. Set AutoPlay (Autorun) features to disabled. This keeps the Conficker malware from spreading by using the AutoPlay features that are built into Windows.

To do this, follow these steps: 1. In the same GPO that you created earlier, move to one of the following folders: * For a Windows Server 2003 domain, move to the following folder: Computer Configuration\Administrative Templates\System * For a Windows 2008 domain, move to the following folder: Computer Configuration\Administrative Templates\Windows Components \Autoplay Policies 2. Open the Turn off Autoplay policy. 3. In the Turn off Autoplay dialog box, click Enabled. 4. In the drop-down menu, click All drives. 5. Click OK.

Task 4. Disable the local administrator account. This blocks the Conficker malware from using the brute force password attack against the administrator account on the system.

Note DO NOT follow this step if you link the GPO to the domain controller’s OU because you could disable the domain administrator account. If you have to do this on the domain controllers, create a separate GPO that does not link the GPO to the domain controller’s OU, and then link the new separate GPO to the domain controller’s OU.

To do this, follow these steps: 1. In the same GPO that you created earlier, move to the following folder: Computer Configuration\Windows Settings\Security Settings\Local Policies\Security Options 2. Open Accounts: Administrator account status. 3. In the Accounts: Administrator account status dialog box, click to select the Define this policy check box. 4. Click Disabled. 5. Click OK. 5. Close the Group Policy Management Console. 6. Link the newly created GPO to the location that you want it to apply to. 7. Allow for enough time for Group Policy to update to all computers. Generally, Group Policy replication takes five minutes to replicate to each domain controller, and then 90 minutes to replicate to the rest of the systems. A couple hours should be enough. However, more time may be required, depending on the environment. 8. After the Group Policy has propagated, clean the systems of malware.